How are the following calculations are made?
When income increased by 10%, the quantity of memberships of athletic clubs increased by 15 percent, the quantity demanded of spring water increased by 5 percent, and the quantity demanded of soft drinks decreased by 2 percent. Use the
a. Is club membership a normal or an inferior good?
b. Is demand for club membership income elastic or income inelastic?
c. Is spring water a normal or an inferior good?
d. Is soft drink a normal or an inferior good?